1. Field of the Invention
The present invention relates to a method of track jumping in an optical disc drive, and more particularly, to a track jumping method for performing stable jumps against exterior effects such as disc eccentricity at the time of jumping a small number of tracks in an optical disc drive.
2. Description of the Related Art
The bang-bang control method is known as a typical track jump control method. It has such advantages in that it is simple and readily realized even under non-linear characteristic of an optical disc drive position sensor. However, as optical disc drives have been developed to have high speed and high density, a need exists for a track jump control device for performing more stable and high speed track jumps.
FIG. 1 is a block diagram illustrating a conventional track jump control device. Referring to FIG. 1, a switch (SW) of a conventional track jump control device is switched to operate in either a track follow mode or a track jump mode according to a switching command signal to drive the switch (SW) as shown in FIG. 2A (a). In other words, the track follow mode becomes an operation mode when the switch (SW) is switched to S1, and the track jump mode becomes an operation mode when the switch (SW) is switched to S2 in response to a track jump command provided from an external source. In a track jump mode, a power driver generates a drive signal (trd) which is output to a pickup actuator. As the pickup actuator operates according to the drive signal (trd), an optical spot jumps from one track to the next. Thus, a relative position (y1) of the optical spot with respect to disc tracks varies as shown in FIG. 2A (b). In this case, a tracking error sensor generates a tracking error (y2) as shown in FIG. 2A (c). In FIG. 2A (d) an example of the pickup drive signal (trd), which is provided to the pickup actuator in response to the track jump command, is shown. In FIG. 2B disc eccentricity and an example of the pickup drive signal at the time of a track jump are shown.
Considering only a standard eccentricity frequency, the following relationship exists between eccentricity (xecc) and eccentricity velocity (Vecc).
xecc=A sin(t)xe2x80x83xe2x80x83(1)
Vecc=A cos(t)xe2x80x83xe2x80x83(2)
The time at which a jump is commenced is determined independently of the eccentricity. Thus, the tracking error needs to be controlled to fall within half the width of a track at the end of a bang-bang operation. In addition, in order to perform stable pull-in operation, a track over-run at the moment of the pull-in in a bang-bang jump needs to be reduced as much as possible.
However, according to the above method, the pull-in operation may be unstable due to an increase in the tracking error at the end of the bang-bang jump when a large eccentricity is generated or a large exterior effect is provided.
Also, according to the above method, when the eccentricity velocity increases in a high speed spindle drive, it is necessary to control such that a step jump is completed within a short time period by reducing the width of a bang-bang pulse. However, there is a problem such that a track over-run may readily occur when the tracking error at the time of the pull-in has a large initial value.
To solve the above problems, it is an objective of the present invention to provide a track jump control device which makes it possible to perform a high speed jump and to reduce overshoot at the time of the pull-in for the case of a disc drive with a large eccentricity.
It is another objective of the present invention to provide a track jump control method applicable to the above device.
Accordingly, to achieve the first objective, there is provided a track jump control device for jumping an optical spot from one track to another track in an optical disc drive, comprising an optical spot position command generator for generating predetermined optical spot position command data to designate the position of an optical spot every predetermined sampling period by commencing operation in response to a track jump command provided from an external source and for generating switching control polarity data for switching control, an adder for subtracting tracking error data from the optical spot position command data, and a switching unit for generating the optical spot position command data with a polarity which is left intact or reversed in response to the switching control polarity data.
Also, the track jump control device further includes a linearization unit for generating linearized tracking error data by performing linearization with respect to a tracking error value generated in and output from a tracking error sensor, wherein the adder preferably subtracts the linearized tracking error data from the optical spot position command data.
The switching unit preferably includes a first amplifier for outputting the optical spot position command data with a first polarity, a second amplifier for outputting the optical spot position command data to a second polarity having a polarity opposite to the first polarity, and a switch for being switched to an output of the first amplifier in response to polarity data with a first logic level and for being switched to an output of the second amplifier in response to polarity data with a second logic level opposite to the first logic level.
The predetermined optical spot position command data preferably is cut at a time sufficiently prior to the commencement of the pull-in, at a portion at which the tracking error exceeds a predetermined level.
To achieve the second objective, there is provided a track jump control method for jumping an optical spot from one track to another track in an optical disc drive, comprising the steps of (a) generating predetermined optical spot position command data to designate the position of an optical spot every predetermined sampling period by commencing operation in response to a track jump command provided from an external source, and generating switching control polarity data for switching control, (b) subtracting tracking error data from the optical spot position command data, and (c) outputting the optical spot position command data with a polarity which is left intact or reversed in response to the switching control polarity data.